Why U.S. Regulators Allow Pig Organs In People But Bar Growing Human Organs Inside Pigs

In November 2025, surgeons in Maryland transplanted a gene-edited pig kidney grown in a pig into a living patient — one of six participants in the first clinical trial testing pig-to-human kidney transplants. The kidney was engineered to better match human biology and to address the chronic shortage of donor organs.

Why This Matters

More than 100,000 Americans remain on transplant waiting lists, and thousands die each year before a suitable organ becomes available. Xenotransplantation — transplanting organs or tissues across species — has reemerged as a practical response to that shortage. But while regulators have moved cautiously forward with gene-edited pig organs, they have kept funding paused since 2015 for research that would grow organs made of human cells inside animals, citing ethical concerns.

Two Scientific Paths

Gene-Edited Pig Organs: Researchers edit pig genes and sometimes add selected human genes to reduce immune rejection. Early clinical work has shown promise but also limits: transplanted pig kidneys have required powerful immunosuppressants and, in at least one case, a pig kidney had to be removed after function declined nine months post-transplant.

Human Organs Grown in Animals: The alternative approach aims to disable the embryonic development of a specific organ in an animal (for example, a pig) and then inject human stem cells so those cells produce a genetically human organ matched to a patient. In theory, such organs would reduce or eliminate immune rejection. Technically, this approach faces challenges — notably differences in developmental timing between species — but it has precedent: researchers previously grew a mouse pancreas inside a rat.

Ethical Concerns Behind the NIH Pause

In 2015 the National Institutes of Health paused funding for experiments that insert human stem cells into animal embryos to examine ethical risks. Policymakers worried human cells might migrate into an animal's brain and alter cognition. The NIH specifically warned of possible "alterations of the animal's cognitive state," and advocacy groups argued that animals with humanlike awareness might require protections accorded to human research subjects.

Core concern: If animals developed higher cognitive capacities from human cells, they might attain a higher moral status and require stronger protections.

Why That Reasoning Is Contestable

Critics argue the NIH's rationale conflates moral status with the presence of a few human cells and treats species membership inconsistently. In practice, protections in research often follow species lines: humans are protected because they are human, not because every human shares a particular cognitive profile. By the same token, pigs genetically modified to reduce immune conflict already contain human genes yet are not treated as "half-human."

If moral status rested solely on cognitive capacities such as self-awareness, then inserting cells from other cognitively capable animals (for example, primates or dolphins) should raise equivalent alarm — but regulators have not treated these scenarios the same way. The ethical picture is more complex: legitimate questions include animal welfare, the morality of using sentient animals as organ sources, and the long-term ecological or biosafety risks of chimeric research.

A Path Forward

A clearer ethical and regulatory framework would separate scientifically plausible cognitive risks from symbolic or species-based anxieties. Practical safeguards could include strict limits on the contribution of human cells to brains, transparent oversight, strong animal welfare protections, phased pilot studies, and independent ethical review. Such a framework would aim to balance urgent human needs — reducing deaths on transplant waiting lists — with robust protections for animals and society's ethical commitments.

Conclusion

The contrast between permitting gene-edited pig organs and pausing funding for human-animal chimera research reflects a mixture of scientific caution and moral ambiguity. Thoughtful, evidence-based policy could allow ethically constrained research to continue while guarding against real and plausible harms to cognition, welfare, and public trust.

Source: Republished from The Conversation. Written by Monika Piotrowska, University at Albany (SUNY).